Cerogamasus, a New Genus of Parasitinae Mites, with Description of Four New Species from China (Acari: Parasitiformes: Parasitidae)

Simple Summary The present study describes a new genus, Cerogamasus gen. nov., and four new species, Cerogamasus tibetensis Jin & Yao sp. nov., Cerogamasus anhuiensis Jin & Yao sp. nov., Cerogamasus guizhouensis Jin & Yao sp. nov. and Cerogamasus multidentatus Jin & Yao sp. nov. Cycetogamasus coreanus Athias-Henriot, 1980, is transferred from the genus Cycetogamasus to Cerogamasus gen. nov. An identification key to the known species of new genus is provided. Abstract The new genus, Cerogamasus gen. nov., with the type species Cerogamasus tibetensis sp. nov., is established. The new genus is easily distinguished from other genera of Parasitidae because the dorsal idiosoma in both sexes bears more than 40 pairs of setae, of which fewer than 7 pairs of podonotal setae are smooth; the seta z5 of the dorsal hexagon is similar to j5 and j6 in form (pilose or distally pilose) while different in length (z5 longer); the seta al of the palpfemur is pectinate, and al1 and al2 of the palpgenu are entire; the gnathotectum is trispinate; peritrematal shields in females are posteriorly free; and the palptrochanter in males has a pointed ventral protuberance. C. anhuiensis sp. nov., C. guizhouensis sp. nov. and C. multidentatus sp. nov. are described based on adult samples; C. tibetensis sp. nov. is described based on deutonymph and adult samples. Cycetogamasus coreanus Athias-Henriot, 1980, is transferred to Cerogamasus gen. nov. as a new combination.


Introduction
The Mesostigmata is a large mite order corresponding to about 20% of all known mite species [1].The family Parasitidae Oudemans, 1901, is among the most common and widely distributed families of Mesostigmata [1,2].The mites of the family occur in soil and decaying organic material such as manure, debris and compost; some species are found on the body surface of birds or arthropods and in carcasses of mammals [3][4][5].They are essentially predatory and feed upon other microarthropods and nematodes, including their eggs [3,6].Parasitidae comprises more than 500 species and 46 genera in two subfamilies: Parasitinae Oudemans, 1901 (23 genera), and Pergamasinae Juvara-Bals, 1972 (23 genera) [7][8][9][10].
Four new species were found during a current study of the Chinese Parasitidae.According to the key for the families of the order Mesostigmata [22] as well as the definitions provided by Evans and Till [14] and Hrúzová and Fend'a [5], we have placed them in the subfamily Parasitinae.The aim of this study is to describe a new genus, Cerogamasus, and four new species, C. tibetensis, C. anhuiensis, C. guizhouensis and C. multidentatus, of Parasitidae from China and thus contribute to the knowledge of the fauna of Mesostigmata in Asia.

Materials and Methods
Individuals of four new species were extracted from decaying leaves, moss, weed piles or rotten wood from Berlese-Tullgren funnels for 12-24 h; placed in 75% alcohol; cleaned in Nesbitt's solution; and then mounted on slides in Hoyer's medium (distilled water/arabic gum/chloral hydrate = 5:3:20:2) for later identification [1].All specimens were deposited in the Institute of Entomology, Guizhou University, Guiyang, China (GUGC).
Line drawings were prepared with the aid of a drawing tube attached to a phasecontrast Nikon Ni E microscope with DIC optics; photographs were taken using a camera (Nikon DS-Ri 2) attached to a Nikon Ni E microscope with DIC optics and figures were edited with Adobe Photoshop CC 2021.Measurements were carried out on all available specimens, the measuring followed that in [25] and all measurements were given in micrometres (µm).
The system of idiosomal setal nomenclature followed [3].Terminology for the palp chaetotaxy followed [28], and then adenotaxy (idiosomal glands) and poroidotaxy (lyrifissures) followed [29,30].The description of the males and deutonymphs omitted the features common with the females.The diagnosis of Cerogamasus gen.nov. in both sexes: dorsal idiosoma well sclerotized and reticulated, bearing more than 40 pairs of setae, of which fewer than seven pairs of podonotal setae are smooth; seta z5 of the dorsal hexagon similar to j5 and j6 in form (pilose or distally pilose), but different in length (z5 longer); seta al of palpfemur pectinate and al1 and al2 of palpgenu entire; corniculi short; gnathotectum three prongs (but four prongs in the male of C. multidentatus sp.nov.); fixed digits of chelicera with more than seven teeth.

Family
In the female: podonotal and opisthonotal shields separate; metasternal shield separated from sternal and epigynal shields; epigynal shield subtriangular and separated from opisthogastric shield; opisthogastric shield bearing at most ten pairs of ventral setae; peritrematal shields posteriorly free; movable digits of chelicerae with more than seven teeth.
In the male: Holodorsal shield with a transverse suture in central region; the base of tritosternum reduced; the venter of hypostome elevated forward and forming a protuberance; setae h1, h2 and h3 on the protuberance, seta pcx near the base; palptrochanter with a pointed and horn-like ventral protuberance.Femur II with a main spur (proximal) and an axillary process (distally), genu II with or without spur, and tibia II with a spur.
Etymology.The name of the genus is derived from "cero-", meaning "horn", and refers to the horn-like process on the palp trochanter in males, with "-gamasus" referring to gamasine mites (masculine).
Other  Diagnosis.Both sexes: dorsal setae z1, z2, s1, s2, r4, r5 and r6 smooth; gnathotectum emerging from denticulate base; seta pcx on gnathosoma pilose; setae v1 and v2 on palptrochanter equal in size.In the female, endogynium with a saccate structure, its centre having a floriform structure; opisthogastric shield bearing ten pairs of ventral setae, of which four pair distally pilose.In the male, opisthogastric region with eight pairs of setae distally pilose; movable digit with a big blunt tooth and several small teeth; genu II and tibia II with a spur.
Other stages.Unknown.
Etymology.The new species name is derived from the type locality Guizhou Province (guizhouensis).
Differential diagnosis.C. guizhouensis sp.nov. is morphologically similar to C. tibetensis sp.nov. in the setal form with regard to the opisthonotal shield, the setal number on the opisthogastric shield of female and opisthogastric soft cuticle and the genu II and tibia II of male with a spur.However, C. guizhouensis sp.nov. is different from C. tibetensis sp.nov.as follows: (1) dorsal seta z2 smooth and s6 distally pilose, vs. seta z2 distally pilose and s6 smooth in C. tibetensis sp.nov.; (2) gnathotectum emerging from denticulate base, vs. nude base in C. tibetensis sp.nov.; (3) seta pcx on gnathosoma pilose, vs. smooth in C. tibetensis sp.nov.In addition, the differences between them in the female are as follows: (1) presternal platelets one pair, vs. three pairs in C. tibetensis sp.nov.; (2) opisthonotal shield with four pairs of pilose setae, vs. one pair in C. tibetensis sp.nov.; (3) seta v1 and v2 on palptrochanter stout and equal in length, vs. seta v1 slender and about twice as long as seta v2 in C. tibetensis sp.nov.The difference between them in the male is as follows: (1) opisthogastric region with eight pairs of pilose setae, vs. six pairs in C. tibetensis sp.nov.Diagnosis.Both sexes: dorsal setae z1, s1, s2, s6, r4, r5, R1, R2, R3 smooth; gnathotectum emerging from the nude base; seta pcx on gnathosoma smooth; setae v1 on palptrochanter longer than v2.In the female, endogynium with a saccate structure, distal with an inverted V-shaped structure, the base with several teeth, each side flanked with two lamellar structures; opisthogastric shield bearing nine pairs of ventral setae, of which four pairs are distally pilose.In the male, opisthogastric region with eight pairs of distally pilose setae; seta v2 on palptrochanter modified to button-shaped; movable digit with a big blunt; genu II and tibia II without spur.
Other stages.Unknown.
Etymology.This species is named after its endogynium with many teeth (multidentatus).Differential diagnosis.C. multidentatus sp.nov. is morphologically similar to C. tibetensis sp.nov. in setal form and number on podonotal shield, the number of chelicera and presternal platelets, and to the setal form of subcapitulum.However, the differences between them in the female are as follows: Male (n = 3).Dorsal idiosoma (Figure 11A).Idiosoma length: 746-768; width: 532-545.Holodorsal shield covering entire dorsum; a suture closely anterior to seta J1.All setae on the shield; setal form as in female.Legs.Lengths of legs: I 755-799, II 514-553, III 469-501, IV 728-761.Femur II with a main spur (proximal) and an axillary process (distally); genu II and tibia II without spur (Figure 11G).
Other stages.Unknown.Etymology.This species is named after its endogynium with many teeth (multidentatus).

Discussion
The family Parasitidae comprises two subfamilies: Parasitinae and Pergamasinae.The generic concept of this family is not stable.The number of genera varies depending on authors and their view on the systematics of the family, especially on the rank of taxa [34].The most comprehensive monograph on mites of Parasitidae contains 45 genera (23 genera within Parasitinae and 22 genera within Pergamasinae [7]).Juvara-Bals [8] described a new genus: Occigamasus Juvara-Bals, 2019 (Pergamasinae).Makarova [9] described another genus: Thalassogamasus Makarova, 2019 (Parasitinae).Yao et al. [10] indicated Taiwanoparasitus Tseng, 1995, a newly synonymized with Psilogamasus.The family now contains 46 genera, Parasitinae and Pergamasinae, each with 23 genera.These genera are easily distinguished from the new genus by the female with two shields; dorsal idiosoma in both sexes bears more than 40 pairs of setae, of which fewer than 7 pairs of podonotal setae are smooth; seta z5 of dorsal hexagon similar to j5 and j6 in form (pilose or distally pilose); seta al of palpfemur pectinate, al1 and al2 of palpgenu entire; gnathotectum trispinate; female peritrematal shields posteriorly free; male palptrochanter with one pointed ventral protuberance.
The placement of the species Cycetogamasus coreanus needs some discussion.This species was previously known only from the adult females collected from litter and moist black humus in Korea [32].The original description of C. coreanus is not very detailed or adequately illustrated.Recently, C. coreanus has been redescribed [33].The genus Cycetogamasus was established by Athias-Henriot with Cycetogamasus diviortus Athias-Henriot, 1967, as its type species [32].The main characteristics of the females of this genus are the presence of the cingulum, gland pores gv2 with one or two openings and a movable digit with three teeth.Cycetogamasus diviortus is different from those species, especially the type species C. diviortus, in the following characteristics: absence of the cingulum, many teeth on the movable digit of the chelicera and gland pores gv2 with three openings or not seen [32,33].The common features of female C. coreanus with Cerogamasus gen.nov.are the following: female peritrematal shields free posteriorly; dorsal setae z5, j5 and j6 pilose or distally pilose; less than seven pairs of podonotal setae smooth; trochanter of palp with one pointed ventral protuberance in the male.We conclude that C. coreanus must be included in the new genus Cerogamasus.
The geographical distribution of Cerogamasus gen.nov. is currently limited to Asia, i.e., China, Republic of Korea and North Korea [32,33].Because only one deutonymph was collected from the moss, we are not confident about the true habitat of the species in the genus.The apparent absence of the juveniles from the decaying leaves, weed pile or rotten wood of the adult habitat might suggest another habitat for development of juveniles [32,33].
If immatures also inhabit decaying leaves, moss, weed piles or rotten wood, their absence may be explained by two reasons: the collector picked up the large individuals (adults) which were easily detectable with the naked eye, or almost all immatures had already reached adulthood before the moment of sampling [3,35,36].The chelicerae of the species in the genus have several small teeth and look very robust, which is more suitable for crushing solid food rather than sucking fluids [1,37,38].Catching live individuals and rearing them in the laboratory would uncover the feeding habits of this species.
The presence of a swollen protuberance on the venter of the palptrochanter in the male may be an adaptation for optimal feeding [1,36].Having most of the dorsal shield setae and leg setae relatively stout and pilose distally may give the mite an advantage to move freely among decaying leaves, moss, weed piles and rotten wood [39,40].
stages.Unknown.Etymology.The new species name is derived from the type locality Anhui Province, China (anhuiensis).Differential diagnosis.C. anhuiensis sp.nov. is morphologically similar to C. tibetensis sp.nov. in the setal form with regard to dorsal shields, the number of teeth on the cheliceral and tibia II with a spur in males.However, C. anhuiensis sp.nov.female is different from C. tibetensis sp.nov.as follows: (1) opisthogastric shield bearing nine pairs of setae, vs. ten pairs in C. tibetensis sp.nov.; (2) gnathotectum emerging from denticulate base, vs. nude base in C. tibetensis sp.nov.; (3) seta v2 on palptrochanter stouter than v1, vs. seate v1 and v2 equal in size in C. tibetensis sp.nov.; (4) seta pcx on gnathosoma pilose, vs. smooth in C. tibetensis sp.nov.The differences between them in the male are as follows: (1) opisthogastric region with one pair of setae distally pilose, vs. six pairs in C. tibetensis sp.nov.; (2) genu II without spur, vs. a spur in C. tibetensis sp.nov.3.1.3.Cerogamasus guizhouensis Jin & Yao sp.nov.